Superhard materials have proven to be useful in a wide variety of applications. For example, cutting elements used in earth-boring tools often include a polycrystalline diamond (PCD) material, which may be used to form polycrystalline diamond cutters (often referred to as “PDCs”). Such polycrystalline diamond cutting elements are conventionally formed by sintering and bonding together relatively small diamond grains or crystals under conditions of high temperature and high pressure in the presence of a catalyst (e.g., cobalt, iron, nickel, or alloys and mixtures thereof) to form a layer of polycrystalline diamond material on a cutting element substrate. These processes are often referred to as high temperature/high pressure (or “HTHP”) processes. The cutting element substrate may comprise a cermet material (i.e., a ceramic-metal composite material) comprising a plurality of particles of hard material in a metal matrix, such as, for example, cobalt-cemented tungsten carbide. In such instances, catalyst material in the cutting element substrate may be drawn into the diamond grains or crystals during sintering and catalyze formation of a diamond table from the diamond grains or crystals. In other methods, powdered catalyst material may be mixed with the diamond grains or crystals prior to sintering the grains or crystals together in an HTHP process.
Earth-boring tools for forming wellbores in subterranean earth formations that may include a plurality of cutting elements secured to a body include, for example, fixed-cutter earth-boring rotary drill bits (also referred to as “drag bits”). Such fixed-cutter bits include a plurality of cutting elements that are fixedly attached to a bit body of the drill bit, conventionally in pockets formed in blades and other exterior portions of the bit body. Other earth-boring tools may include rolling cone earth-boring drill bits, which include a plurality of cutters attached to bearing pins on legs depending from a bit body. The cutters may include cutting elements (sometimes called “teeth”) milled or otherwise formed on the cutters, which may include hardfacing on the outer surfaces of the cutting elements, or the cutters may include cutting elements (sometimes called “inserts”) attached to the cutters, conventionally in pockets formed in the cutters. Cutting elements that include superhard materials increase the useful life of the earth-boring tools to which they are attached because the superhard materials increase the strength and abrasion resistance of the tools.
Some superhard materials have desirable properties that render them useful in still other applications. For example, the high strength and abrasion resistance of such materials renders them useful in grinding, polishing, and machining applications. Increased thermal conductivity of some superhard materials renders them useful as particles dispersed in lubricants, such as motor and pump oils, because such lubricants often serve to cool the parts they lubricate. Furthermore, increased electrical conductivity of some superhard materials renders them useful as fillers in polymers and elastomers, where increased electrical conductivity in at least some portion of the polymers and elastomers is desirable.
Some attempts have been made to enhance or alter the properties of superhard materials through layering other materials thereon. For example, Core-Shell Diamond as a Support for Solid-Phase Extraction and High-Performance Liquid Chromatigraphy, 82 Analytical Chem. 4448 (Jun. 1, 2010), by Gaurav Saini, David S. Jensen, Landon A. Wiest, Michael A. Vail, Andrew Dadson, Milton L. Lee, V. Shutthanandan, and Matthew R. Linford discloses, among other things, layer-by-layer deposition of an amine-containing polymer and nanodiamond on an amine functionalized microdiamond.